Signaling system



G. P. ADAIR Dec. 1O, 1929.

SIGNALING SYSTEM Filed Feb. 18 1928 AMPL/F/ER Invent-or: George F1 AdamHus Attorney.

Patented Dec. 10, 1929 UNITED ST ES PATENT OFFICE I GEORGE I. ADAIB, OFBGHENECTADY, NEW YORK, 'ASSIGNOR '10 GENERAL ELECTBIC COMPANY, ACORPORATION 01' NEW YORK SIGNALIN G SYSTEI Application filed February18, 1928. Serial No. 255,484.

My invention relates to signaling systems and more particularlyto highfrequency communication systems of the duplex type in which automaticmeans are provided for controlling the volume of the signal which isreceived from remote points and for protecting the receiving equipmentagainst energy which reaches it from the associated transmitter.

Still more particularly my invention relates to systems of the typedisclosed in application Serial N 0. 161,191 of Lester F. Bird, filed January'li, 1927 and which is assigned to the same assignee as thepresent application. In thatapplication a device is disclosed comprisinga three element electron discharge device, the anode-cathode circuit ofwhich comprises a shunt to the receiving channel. The potential of thegrid of this device is controlled by a resistance whichis connected inseries with the discharge path of both the detector of the receivingcircuit and the oscillation generator of the associated transmitter. Inthis way the impedance of the three element device may be controlledboth in response to the signal intensity as indicated by the magnitudeof the detector anode current and totthe functioning of the oscillationgenerator. Thus this shunt connected control device in the receivingcircuit serves both to protect the receiver against energy which reachesit from the associated transmitter and also to control the volume of thereceived signal.

While the device disclosed by Mr. Bird in the above application hasproved to be a very satisfactory onein commercial practiceIhave foundthat certain simplifications in the circuit may be made which result inimproved operation of the system as a whole and at the same time inreduced cost of construction and maintenance.

The novel features which I believe to be characteristic of m inventionwill be set forth with particufarity in the appended claims. Myinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages thereof may bestbe understood by reference to the following description taken inconnection with the accompanying drawmg, in WhlCll the single figurerepresents an embodiment of my invention.

Referring to the drawing 1" represents a portion of the transmittercircuit and 2 the essential elements of the associated receiving c rcuitto which I have applied my invention. In the receiving circuit I haveshown an electron discharge device 3, which is employed as a detector.The input circuit to this detector is supplied with received signalcurrents through a channel which includes the conductors 4, which leadto any suitable .antenna or wire line circuit, such as a powerdistribution system from which the signals are received, 6. The seconary winding of this transformer is connected through condensers 7 and 8the latter of whichis connected in parallel with resistance 17 to thegrid and cathode respectively of the electron discharge devlce 3. Theoutput currents from this discharge device are supplied from the anodec1rcuit,thereof through the transformer 9,

hybrid coil 10 and output circuit 11 to anythereof through the chokecoil 15, source of potential 16, resistance 17, conductor 18,spacebetween the cathode and anode of control electron discharge device19, conductor 20 and the space between the cathode and anode ofdischarge device 12. Signal currents from any suitable signaling deviceor telephone instrument may be impressed upon the grid of the controldevice 19 through the circuit 11, hybrid coil 10 and amplifying means21. These currents will also be caused laybrid coil 5 and transformer tomodulate the currents which are produced b153 1 the oscillationgenerator 12 by any suite means, not shown. One means whereby thismodulation may be eflected is illustrated in Patent No. 1,696,590, L. F.Bird, issued December 25, 1928. Condenser 28 is connected between theanode and cathode of device 19 to prevent modulation of the transmitteroutput currents by this device. Energy is supplied for heating thecathodes of the discharge devices .12 and 19 through suitable cathodetransformers 22 and 23.

In the receiving circuit an electron discharge device 24 of the twoelement type, or of the three element type, in which the grid and anodeare connected together to constitute a single electrode is connected inshunt with the receiving circuit and hence in shunt with the tunedcircuit 25, which comprises the input circuit of the detector 3. Theanode circuit of the device 24 is suitably biased with respect to thecathode thereof by means of a source of potential 26, such that thedevice has no substantial effect upon signals which are received havingsubstantially normal intensity. This bias, however, is such that it isovercome by signals of greater than normal intensity, which therebycause the impedance between the anode and cathode of this device to bediminished. This diminution of the impedance causes the device 24 tobecome an effective bypassfor a portion 0 the signal currents'and ashunt upon the tuned circuit 25. The sharpness of the tuning of circuit25 is then lessened and this eflect together with that of bypassing aportion of P the signal currents serves to diminish the intensity of thesignals whichreach the grid of detector 3. The impedance of this shuntpath will of course be dependent upon the intensity of the receivedsignal and will vary therewith. .Thus to signals which are receivedhaving normal intensity, the device 24 is ineffective to produce anysubstantial diminution thereof, but as soon as signals of greater thannormal intensity are'received the impedance of the device 24 becomesdiminished, thereby causing a portion of these signals to .be shortcircuited through the device 24, and

the tuned circuit to be affected. In this way a very effective volumecontrol of the received signals may be had. 7

This device is also caused to respond to operation of the transmittingcircuit. It will be noticed that the resistance 17 is connected betweenthe cathode and anode of the device 24 and is also connected in serieswith the discharge path of the oscillation generator 12.

' Thus whenever current flows in the discharge path of the oscillationgenerator a potential will appear across the resistance 17 having theolarity indicated on the drawing and tending to drivethe anode thereofstrongly positive with respect to the cathode. In t is way the impedanceof device 24 is greatly shunt circuit of low impedance to currents whichreach the receiver and also causes the tuned circuit to be affected inthe manner described. '].lhus the receiving circuit is renderedinsensitive to excessive and disturbing potentials which may rea ch itfrom the transmitting circuit during operative periods thereof.

Current is caused to flow in the discharge path of the oscillationgenerator by means of the control device 19 upon which the voicecurrents are impressed. This device normally has sufiicient impedancebetween its cathode and anode to preclude the flow of anode currentthrough the oscillation generator and hence to preclude the operation ofthe device 12. When the operator speaks into the microphone voicecurrents will be supplied through the audio amplifier 21 to the grid ofdevice 19. The impedance between the anode andcathode thereof will thenbe reduced and current will becausedto flow in the circuit previouslytraced including'the anode, cathode circuit of the device 12 and theresistance 17 thereby causing the initiation of high fref ceivingcircuit and the tuning of the circuit to be affected.

Thus the device24 serves in a dual capac- 'ity, acting as a volumecontrol means during eriods of reception of signals from a remotestatiofi'and as a means for rotecting the re ceiver against excessive andisturbing v'oltages which reach it from the transmitter during periodsof transmission. The circuits of device 24 may be separately adjusted ina "manner which permits most efficient operation of the device in bothof its dual functions. Thus the source of potential 26 may be varied ina manner to permit best operation of the tube as a volume control deviceand the value of resistance 17 may be adjusted to permit best operationas a protective device.

I The operation of the device is entirely independent of that of thedetector and hence. it is not subjected to any irregularities in thefunctioning of that device. A normal detector circuit may be employed.It will be noticed that the cathodes of the control device and detectorare always at the same potential. Hence a common cathode source ofpotential may be employed and the expense of providing and maintaining aseparate battery for each device is eliminated.

While I have shown and described a single embodiment of my invention itwill, of course, be understood that I do not wish to be limited theretosince many modifications, both in the circuit arrangements and in theinstrumentalities employed maybe made without departing from the spiritand scope of my in vention as set forth in the ap ended claims.

What Iclaim as new and esire to secure by Letters Patent of the UnitedStates, is:

1. In a signaling system, a receiving circ'uit, a transmitting circuit,an electron discharge device having an anode and a cathode, the spacebetween said anode and cathode being connected in shunt with saidreceiving circuit and the impedance thereof being variable in responseto the intensity of the received signals, and means responsive to operation of said transmitting circuit for impressing a potential upon saidanode with respect to said cathode thereby to diminish the impedance'ofsaid discharge device.

2. In a signaling system, a receiving circuit, a transmitting circuit,an electron, discharge device having an anode and a cathode, the spacebetween said anode and cathode being connected in shunt with saidreceiving circuit, means for biasing said anode with respectto saidcathode such that said device has substantially no effect upon receivedsignals of normal intensity but has diminishing impedance to signals ofgreater than normal intensity, aresistance connected between said anodeand cathode and means responsive to operation of said transmittingcircuit for causing a current to flow through said resistance todiminish the impedance of said discharge device thereby to effect theintensity of currents flowing through said receiving circpit.

3. In a signalingsystem, a receiving circuit and a transmitting circuit,said transmitting circuit including a normally inoperative electrondischarge oscillation generator,

an electron discharge device connected in shunt with said receivingcircuit having an anode and cathode, means for blasm sald anode withrespect to said cathode suc that said device has substantially no eflectupon .received signals of normal intensity-but has diminishing impedanceto currents. of intensitygreater than normal, and a resistance connectedbetween said anode and cathode, said resistance beingalso connected inseries with the discharge path of said oscillation generator' wherebysaid receiving circuit is rendered insensitive dur ng operatlve-perlodsof said osclllatlon generator.

4. In a signaling system, a transmitter and a receiver, a tuned inputcircuit to said receiver, a two electrode electron discharge devicehaving an anode and cathode connected in shunt with said tuned circuit,said device havin impedance such that it has no substantial 'eEect uponreceived signals of normal intensity but which diminishes in response tosignals of intensity greater than normal, and means for producing. apositive. potential upon said anode with respect to said cathoderesponsively to operation of said transmitter to diminish the impedanceof said device,

thereby to cause said device to constitute a low impedance shunt acrosssaid rec'eiving circuit and to affect the tuning of said input circuit.

